Polyphenylene sulfide (hereinafter may be abbreviated as PPS) resins have properties suitable for engineering plastics such as excellent heat resistance, chemicals resistance, solvent resistance and electric insulation, and are used mainly for injection molding and extrusion, to be used as various electric and electronic parts, mechanical parts, automobile parts, etc. As resins with such various excellent properties and dispersions thereof, there is a high demand for fine PPS resin particles and dispersions thereof in the paint field, adhesive material field, polymer compound field, etc., but they are presently very difficult to obtain owing to the technical restrictions described below.
As processes for obtaining fine PPS resin particles, several processes as described below are proposed. Patent Document 1 discloses a process for obtaining fine PPS resin particles relatively controlled in particle size by controlling the water content and the vapor phase temperature in the reaction system for producing a PPS polymer. The fine PPS resin particles obtained by this process range from tens of micrometers to hundreds of micrometers in average particle size. Further, Patent Document 2 describes spherical fine PPS particles ranging from 0.1 μm to 100 μm in average particle size, and a production process thereof. The particularly disclosed production process for obtaining the spherical fine PPS resin particles comprises the steps of forming a resin composition with an islands-in-sea structure with PPS as islands and another thermoplastic polymer as sea, and subsequently dissolving and washing away the sea phase. Even this process can provide only relatively large fine particles ranging from several micrometers to tens of micrometers. Furthermore, Patent Document 3 discloses a process comprising the step of wet-grinding a resin dispersed in surfactant-containing water by a grinder such as a vibrating ball mill, to obtain a resin-based powder. This patent document does not particularly disclose the grinding of a PPS resin, and the obtained resin powder is as large as about 5 to 50 μm in average particle size. It is difficult to obtain fine particles of 1 μm or less by merely wet-grinding a resin.
Since the fine PPS resin particles obtained by the prior art are larger than several micrometers as described above, it is difficult to obtain a stable dispersion thereof. In order to obtain a stable dispersion, it is necessary to obtain fine PPS resin particles smaller in particle size. However, any process for obtaining the fine PPS resin particles of 1 μm or less, i.e., sub-micron size necessary for obtaining a stable fine PPS resin particle dispersion and any process for simply and efficiently obtaining the dispersion are not yet established, it is strongly desired to develop practical production processes for obtaining such fine PPS resin particles and a dispersion thereof.    [Patent Document 1] JP 6-298937 A (claim 1)    [Patent Document 2] JP 10-273594 A (Examples 1 and 2)    [Patent Document 3] JP 2003-183406 A (claim 1, “Modes for Carrying Out the Invention”)